arm64: Enable CPU_IDLE in defconfig

This patch enables CPU_IDLE and the generic arm64 cpuidle driver
(ARM64_CPUIDLE).

Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

arch/arm64/configs/defconfig

@@ -45,6 +45,8 @@ CONFIG_CMA=y
 CONFIG_CMDLINE="console=ttyAMA0"
 # CONFIG_CORE_DUMP_DEFAULT_ELF_HEADERS is not set
 CONFIG_COMPAT=y
+CONFIG_CPU_IDLE=y
+CONFIG_ARM64_CPUIDLE=y
 CONFIG_NET=y
 CONFIG_PACKET=y
 CONFIG_UNIX=y